<![CDATA[Proportional-Integral-Derivative (PID) control remains the most widely adopted strategy for regulating induction motor speed in industrial automation, yet its fixed gains often struggle with the time delay and non-linear dynamics of variable-frequency-driven drives. This study analyzes the parametric performance of a PID controller tuned using the Ziegler–Nichols step-response method and implemented on a Mitsubishi MELSEC iQ-F FX5U Programmable Logic Controller (PLC) to regulate a three-phase, 1 HP induction motor through an Altivar ATV310HU40N4E Variable Frequency Drive (VFD). Parameters were derived analytically from the open-loop reaction curve (L = 0.115 s, T = 0.997 s) and then empirically fine-tuned (Kp = 20, Ti = 0.2 s, Td = 0.03 s) to obtain a stable closed-loop response. The system was tested without load at setpoints of 20–50 Hz and under dynamic loading of 0.5–2 N·m applied through a MCA 13I41 - RS0B0 servo motor. Results show the PID controller reduced rise time relative to the open-loop system at low frequencies but produced overshoot up to 97.0% at low setpoints under heavy load, decreasing almost linearly to near 0% at 50 Hz. The open-loop response was essentially overshoot-free but slower to settle at low frequencies. Both configurations converged to a steady-state error not exceeding 0.1 Hz in every test case. These findings indicate that Ziegler–Nichols tuning derived from a single operating point does not generalize well across the setpoint and load range of a variable-frequency drive, and that gain-scheduled or adaptive tuning is recommended for future implementation.]]>
